1. Field of the Invention
The invention is related to the field of valves, and more particularly, to a butterfly valve.
2. Description of the Prior Art
Valves are used in a variety of applications, including in industrial environments, vehicles, buildings and structures, and so forth. A valve is used to regulate the flow of fluids, including liquids, gases, and mixtures thereof. The flow can include particulates in some environments.
Butterfly valves include a generally round flap that is rotated on a shaft, wherein the rotation can move the valve flap to extend across the valve bore, closing the valve, or rotate the valve to extend horizontally, aligned with the bore and opening the valve to fluid flow. The valve flap may be fully aligned with the flow in some embodiments, wherein the valve flap presents a minimal obstruction to the flow and the valve bore is substantially unobstructed. The valve shaft and valve flap can be rotated by any suitable means, including by mechanical linkages, by electromagnetic devices, and so forth.
Butterfly valves have many advantages. Butterfly valves are simple in design and simple to use. Butterfly valves can offer fast response times. Butterfly valves can offer minimal flow limits or obstructions when fully open. For these reasons, a butterfly valve is highly desirable for regulating flow in ducts.
Butterfly valves feature a minimum of moving parts. But more importantly, butterfly valves have no need for small clearances or tolerances in order to function properly.
An important advantage of butterfly valves is that they are well suited to use with hot fluids, such as hot gases. Butterfly valves are popular for use in engine exhaust systems, as the valve flap can be made to close reliably even in the presence of high temperatures. Further, the valve flap-to-valve-seat contact is simple and does not require high tolerances. Dimensional changes due to heating may not render a butterfly valve inoperable or inefficient. The valve will still operate even where the butterfly valve is subject to thermal expansion and contraction.
However, prior art butterfly valves have drawbacks. Use with high temperature fluids, such as hot exhaust gases, can cause damage. Hot pressurized gases can dry out lubricants and damage bearings. Hot pressurized gases can degrade seal materials, such as rubber or plastics. Thermal expansion can increase friction and binding or cause leakage due to thermal expansion or contraction.